1. Field of the Invention
The present invention relates to an angular rate sensor for use in video camera hand movement detection, motion detection in a virtual reality apparatus, direction detection in a car navigation system, or the like, and more particularly, to a method of manufacturing a small-sized vibration gyro sensor element having a cantilever vibrator, a vibration gyro sensor element, and a method of adjusting vibration direction.
This application claims priority of Japanese Patent Application No. 2004-064239, filed on Mar. 8, 2004, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
So-called a vibration-type gyro sensor (hereinafter, referred to as vibration gyro sensor) has now been widely used as an angular rate sensor for consumer use. The vibration gyro sensor allows a cantilever vibrator to vibrate at a predetermined resonance frequency and detects Coriolis force caused due to influence of an angular rate using a piezoelectric element, thereby detecting the angular rate.
The vibration gyro sensor is advantageous in its simple mechanism, short start-up time, and reduced manufacturing cost, and has now been incorporated in an electronic apparatus such as a video camera, virtual reality apparatus, or car navigation system, to serve as a sensor for hand movement detection, motion detection, direction detection, respectively.
As the electronic apparatuses in which the vibration gyro sensor is incorporated have become increasingly compact and higher performance, the vibration gyro sensor itself is required to be rendered compact and higher performance. For example, miniaturization is required to realize multi-functional electronic apparatus by combining the vibration gyro sensor with various sensors for use in other purposes and mounting them on a substrate.
However, since a vibrator of the vibration gyro sensor is manufactured by shaping a piezoelectric material obtained by a cutting process with machine work, processing accuracy in the manufacturing process cannot meet the requirement for the above miniaturization, so that desired performance cannot be obtained.
In order to cope with the problem, a piezoelectric vibration angular rate meter, that is, a vibration gyro sensor in which the vibrator is manufactured by forming a thin film made of a piezoelectric material on a single-crystal silicon substrate has been devised (referred, for example, to Jpn. Pat. Appln. Laid-Open Publication Nos. 8-261763 and 8-327364).
The vibrator of the vibration gyro sensor needs to be a regular square pole having a square cross-section in order to detect an angular rate with stable detection accuracy. However, it is physically very difficult to obtain the vibrator as a perfectly regular square pole in the case where the vibrator is manufactured by machine work or in the case where the vibrator is manufactured by processing a single-crystal silicon substrate with a thin-film formation process, so that the manufactured vibrator may have an asymmetrical cross-section.
When a drive signal is applied to such an asymmetrical shaped vibrator to cause self-excited vibration, the vibration direction does not follow the center line of the vibrator, but is inclined relative to the center line of the vibrator. When the vibration direction is inclined as described above, the value of the detection signal to be detected for the angular rate detection becomes inaccurate, leading to an inaccurate angular rate.